As the transmission of data becomes more and more popular in our industrialized society, there is a need to transmit, and hence switch, both voice and data traffic over the same network facility.
Many methods of integrally switching both voice and data are known, however, these methods can cause bottlenecking of a controller, which are of a limited fixed bandwidth and relatively expensive to grow.
The switching network commonly used for high bandwidth switching is the crossbar switch where crosspoints are set by a centralized controller. This centralized control of the crosspoints can result in bottlenecking of the controller, especially at high switching rates. For example, in a typical case, 100 Mbps serial transmission of data and voice frequency on a 128.times.128 crossbar switch, approximately 16,000 crosspoints would have to be set up in about 3 usec. In addition, such a centralized controller would have to store the settings for each slot in a frame requiring a very fast and large memory. To further bottleneck the central controller, the well known switching systems use the controller to assign time slots. More specifically, U.S. Pat. No. 4,445,213 to Baugh et al handles both voice and data, however, a fixed number of time slots for voice or synchronous data are assigned by a centralized controller.
The most relevant art for integrated voice data switching is directed to controlling switching data or voice on a digital loop of a fixed maximum bandwidth. This art supports data in the order of tens of megabits per second. More specifically, U.S. Pat. Nos. 4,445,213 to Baugh et al and 4,251,880 to Baugh et al provide for the integrated transmission of both voice (synchronous data) and data (asynchronous data) between interchangers interconnected by a digital loop of fixed maximum bandwidth. The above cited patents support data rates up to in the order of several megabits per second.
With crossbar switches the number of crosspoint switches grows as the square of the number of input ports. Thus, a 128.times.128 crossbar switch requires (128.sup.2) or 26,384 crosspoint switches. Thus, making large crossbar switches can be very expensive.
Packet switched MINs have been proposed and studied primarily for connecting processors and memories in multi-processor computer systems. These networks use distributed control and can be grown by adding extra stages. However, with the protocols proposed previously, packets have variable delay in passing through the network. This causes clipping due to loss of packets if they are used to switch synchronous traffic such as voice. To obtain small clipping, the networks must be operated at very small load levels so as to reduce the variance of packet delays. Further, it has been shown that if non-uniform traffic occurs in such networks causing hot-spots, network throughput falls drastically, and delays become very large. Such dynamic phenomena would cause unacceptable clipping of synchronous traffic.
There is, therefore, a need to provide a method of integrally switching voice and data with a high bandwidth, reduced clipping, distributed control and inexpensive growth potential.